SUMMARY OF WORK: HIV-1 reverse transcriptase (RT) is a large, complex multi-functional enzyme required for replication of the viral genome. The enzyme will be a target for anti-viral therapy in the future, and in the past it has been by far the most successful target for therapy. The enzyme is responsible for the extreme genetic hypervariability of HIV-1 and, hence, the virus ability to escape drug-mediated suppression in AIDS patients via mutation. Through studies of RT's mechanism, our laboratory, in collaboration with Dr. Kunkel's laboratory, discovered that the mutation propensity is linked to how well the enzyme stays attached to the DNA during replication. Thus, if RT falls off the viral template strand during replication, it tends to make an error (or mutation) at the point where it climbs back on the template and continues replication. This mechanism appears to account for most of the HIV-1 genetic hypervariability. Much insight into the mechanism of falling off has been gained recently by combining structural information on RT with biochemical studies of the wild-type enzyme and enzymes strategically altered in specific amino acid residues that control affinity of binding to the template. We have localized many of the critical template-binding amino acids of the RT to a small region near the polymerase active site known as the Minor Groove Binding Track. This protein motif was first appreciated through molecular modeling conducted by our collaborator, Dr. Darden. These studies of the template binding surface of RT will enable our group, and others, to design drugs that will bind to the enzyme just as tightly as the template and, thus, block the enzyme. Thetemplate-binding surface on RT is considered to be different from those on the surfaces of the cellular DNA polymerases. Therefore, such new inhibitors of RT should be highly specific to RT, as well as highly effective. Studies of this interesting enzyme also will enhance our understanding of other replicative DNA polymerases. Future work will emphasize the role that DNA structure plays in polymerase function. Aims and Accomplishments: Our experimental approach toward drug design for AIDS is through targeting the nucleic acid-binding functions of the essential HIV-1 enzyme known as reverse transcriptase. We have discovered a small region on the surface of the enzyme that mediates nucleic acid-binding. This information can now be the basis for strategic drug-design approaches.